In the mining industry ore is often conveyed over long distances by aerial tramways. Such aerial tramways typically include a plurality of load carrying units or buckets that are filled with ore and attached to a movable haul rope supported from towers which extend over the length of the course over which the ore is to be conveyed.
A typical prior art mining aerial tramway system includes pairs of stationary cables on which the load carrying buckets are mounted by means of rollers. The movable haul rope is connected to each bucket in between the stationary ropes. The buckets are rolled along the stationary ropes by driving the movable haul rope. This system has the disadvantage of requiring three ropes and, more importantly, requiring that each of the load carrying units be provided with sheave assemblies which roll on the stationary ropes. Such sheaves, however, are subject to substantial wear and tear, particularly in dusty and abrasive mining environments.
Aerial tramways are also extensively used in the recreational industry in connection with skiing. Such tramways typically employ a plurality of load carrying passenger units which are attached to a movable haul rope and conveyed over a relatively short distance, for example, one-half to one and one-half miles. While the passenger carrier units of recreational aerial tramways could be changed to ore carrying units, there are numerous differences in mining applications which make conventional passenger carrying aerial tramways not well suited for use in the transport of ore.
In mining applications, ore is often transported over much longer distances, e.g., five-to-twenty miles. Moreover, it is important to maximize the load which can be transported by the tramway, and the presence of substantial airborne dust and debris is extremely hard on equipment.
One approach to increasing the loading or capacity of aerial tramways is to couple the load carrying units of an aerial tramway to pairs of side-by-side, endless haul ropes, as for example is shown in my U.S. Pat. Nos. 4,848,241 and 4,864,937. In my U.S. Pat. No. 4,864,937 the load carrying unit is supported on both the top and bottom portions or stretches of the pairs of haul ropes, which further increases loading capacity, but which also requires the use of sheaves or roller elements on each carrier unit. In the dusty environment of mining and transportation of ore, it is desirable to minimize the number of roller elements or sheaves employed in the tramway system.
In my U.S. Pat. No. 4,848,241 I employ an aerial tramway system in which the load carrying units are detachably mounted to pairs of haul ropes and the speed of the haul ropes is maintained in synchronism by slightly adjusting the diameter of one of the haul rope bull or drive wheels. This approach is entirely adequate for aerial tramway systems designed for transport of passengers since the length of the tramway course is not excessive.
In mining applications, however, it is very difficult to maintain synchronism of two haul ropes over a course length of, for example, 15 miles, using adjustable bullwheels at the ends of the tramway. Moreover, differences in haul rope speed which seem extremely small will accumulate to produce substantial relative displacements of the haul ropes over long courses. As the relative rope displacement increases because of differing rope speeds, the load carrying unit is placed under an increasing torque, which can become very substantial and potentially destructive to grip assemblies and the structure of the load carrying unit itself. Using side-by-side haul ropes to increase loading capacity, therefore, presents significant problems when employed in an aerial tramway system of substantial length.
Accordingly, it is an object of the present invention to provide an aerial tramway system which is suitable for use in ore transport applications over extremely long courses.
Another object of the present invention is to provide an aerial tramway system which is capable of supporting and transporting heavy loads, operates reliably in dusty and debris-filled environments, and is suitable for use over long courses.
Still another object of the present invention is to provide a method for conveying load carrier units of the type used to transport ore which is reliable and economical in its operation and is capable of transporting ore over very long distances.
Still a further object of the present invention is to provide an aerial tramway system and method for operation of the same in which frictional losses over the length of a long course can be compensated for and loading and unloading of ore from the load carrying units can be efficiently accomplished.
Another object of the present invention is to provide an aerial tramway system which is durable, capable of substantial loads, employs haul ropes of moderate size, and uses cable gripping assemblies which have no moving parts.
The aerial tramway system and method of the present invention have other objects and features of advantage which will become apparent from, and are set forth in more detail in, the accompanying drawing and following description of the Best Mode 0f Carrying Out The Invention.